Multiple hotkeys for the same function
At the bottom of the 3D View input list, click on the "Add New" Button. A new command will then appear at the bottom of the listed named "None". 
Click on the triangle to the left of the word "None" to expand the options for the command. Enter this text: view3d.rotate (as shown in the image below) and press Enter. At this point the name of the command will change from "None" to "Rotate View" and you can choose you input command. 


You may also want to double check that the command is not already in use by searching for it in the "Key Bindings" search box at the top of the list. If it is in use you can just disable it by clicking on the checkmark next to its name. That way you won't have any conflicts... hopefully.